The invention concerns mono-component reaction adhesives which can be set by heat. In particular, it concerns a thermosetting reaction adhesive which is suitable for the adhesion of thermo-shrinking molded parts.
The action adhesives are distinguished by the fact that they are present as reaction-capable monomer or oligomer components before setting, which during the adhesion are transformed into high molecular spatially cross-linked polymers. Corresponding to the possible types of the polymerization reaction, reaction adhesives are classified as polymerization, polyaddition and polycondensation adhesives.
Polymerization adhesives are set by radical or ionic polymerization wherein in the first case the radicals necessary for the reaction are generated by UV radiation or by electron rays, but mostly by radical-forming catalysts such as peroxides. Cold setting reaction adhesives are easy to process, but they usually require a long setting time. Thermo- and heat setting reaction adhesive compositions only bind at temperatures from 80.degree. to 200.degree. C., but they supply very high adhesive strengths.
In the case of mono-component reaction adhesives, frequently storage problems occur, because the adhesive components react with each other in the course of time. A remedy is provided by bi- or multi-component adhesive systems, in which the reactive components are only mixed with each other shortly before the bonding.
U.S. Pat. No. 4,548,992 describes a bi-component reaction adhesive in which component I contains an acrylic monomer and an organic peroxide, while component II contains an acrylic monomer and a setting accelerator. Furthermore an unsaturated polyester is present in components I and/or II.
Mono-component reaction adhesives which set radically, are simple to handle but often are not sufficiently stable in storage or are only used for special applications. EP 158 462-A2 discloses adhesive compositions, which harden at room temperature, but are not suitable for bonding metal surfaces.
Typical reactive components of a mono-component reaction adhesive are one or more long-chain ethylene unsaturated polymers, as well as low molecular monomer or oligomer olefins, which cross-link as "bridges" the long-chain polymers with each other during the setting.
DE-OS 17 19 177 describes a thermosetting adhesive which is present on a carrier material in the form of a thermosetting self-adhesive tape. The essential components of this adhesive are an elastomer resistant to oil, an adhesive resin and an unsaturated polyester as the reactive components and a solvent polymerizable therewith. Additional components are optionally a peroxide catalyst or a cross-linking reagent. Preferably, an unsaturated ester monomer is used as the polymerizable solvent. One part of the adhesives described here has the disadvantage that the viscosity increases strongly within a few days and the properties described, e.g. self-adhesive, are lost. The adhesive therefore cannot be stored for long periods. The other adhesive combinations only harden very slowly and are unsuitable for use in an industrial production process.